Polyhydric alcohols such as glycerin have moisturizing properties when applied to the skin and lips. As such, traditional lipsticks and chapped lip products have included polyhydric alcohols such as glycerin in their formulations. Such products are typically waxy solids based on thickening agents such as ozokerite, beeswax, and candelilla wax. For example, U.S. Pat. No. 6,090,386 and U.S. Pat. No. 6,325,995 each describe lipsticks containing about 2-20% glycerin or other hydrophilic moisturizer. However, the products described therein are wax-based, and maintain a hard or durable consistency.
Glycerin-in-oil emulsions which might provide for both increased amounts of glycerin compared to wax-based products and for soft formulations for increased comfort on the lips are known to suffer from stability problems. For example, see U.S. Pat. No. 4,254,104, which describes the failure of prior art attempts to provide stable glycerin-in-oil emulsions with olive oil and surface-active agents. It is thought that the stability problems of glycerin-in-oil emulsions are due at least in part to the increased difference in density between glycerin and oil as compared to water and oil. As a result, soft formulations provided as an alternate to the traditional hard or durable lipstick fail to incorporate glycerin or other hydrophilic moisturizers. For example, see U.S. Pat. No. 4,996,044, which describes soft formulations to be applied to the lips which are free of glycerin or other hydrophilic components.
Glycerin-in-oil emulsions are particularly unstable when exposed to extremes of temperature, and in particular, at higher temperatures and oscillating temperatures involving hot and cold. These temperature extremes and changes may result in separation of phases or breaking of the emulsion. Such stability problems decrease consumer acceptance of glycerin-based products as the consumer may generally consider a product with separated phases or with leaching between phases to be unsatisfactory.
It is therefore an object of the invention to provide cosmetic and therapeutic compositions for application to the outer surface and skin of the face and body, including the lips, wherein the compositions are glycerin-in-oil emulsions with improved stability over time or improved stability when exposed to high temperatures.